Control valve for variable displacement compressor

ABSTRACT

To provide a control valve for a variable displacement compressor, which is capable of promptly restoring the compressor to a predetermined discharge capacity even when the rotational speed of an engine is rapidly changed. In a valve section for controlling the flow rate of refrigerant flowing from a discharge chamber into a crankcase of a variable displacement compressor, a pressure-sensing section is provided in a high-pressure port that receives discharge pressure. In the pressure-sensing section, when a pressure-sensing piston which is larger in pressure-receiving area than a valve element receives a change in discharge pressure caused by a rapid change in rotational speed of the engine, differential pressure is produced between discharge pressure Pd and pressure in a pressure-adjusting chamber, which temporarily produces a force for axially moving the piston. This force is transmitted to the valve element via a shaft, to thereby accelerate the opening/closing motion of the valve element caused by the differential pressure between discharge pressure and suction pressure, whereby the compressor is promptly restored to a predetermined discharge capacity.

CROSS-REFERENCES TO RELATED APPLICATIONS, IF ANY

This application claims priority of Japanese Application No. 2004-239162 filed on Aug. 19, 2004 and entitled “CONTROL VALVE FOR VARIABLE DISPLACEMENT COMPRESSOR” and No. 2004-289520 filed on Oct. 1, 2004, entitled “CONTROL VALVE FOR VARIABLE DISPLACEMENT COMPRESSOR”.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a control valve for a variable displacement compressor, and more particularly to a control valve for a variable displacement compressor, which is mounted on a variable displacement compressor as a component of a refrigeration cycle of an automotive air conditioner, for control of the discharge capacity of the compressor by the differential pressure between discharge pressure and suction pressure.

(2) Description of the Related Art

A compressor used in the refrigeration cycle of an automotive air conditioner, for compressing refrigerant, uses an engine as a drive source, and hence is incapable of performing rotational speed control. To eliminate the inconvenience, a variable displacement compressor capable of varying the compression capacity of refrigerant is employed so as to obtain an adequate cooling capacity without being constrained by the rotational speed of the engine.

In such a variable displacement compressor, a wobble plate fitted on a shaft driven by the engine for rotation has compression pistons connected thereto, and by varying the inclination angle of the wobble plate, the stroke of the pistons is varied to vary the discharge amount of refrigerant.

The inclination angle of the wobble plate is continuously changed by introducing part of compressed refrigerant into a hermetically closed crankcase, and causing a change in the pressure of the introduced refrigerant, thereby changing the balance of pressures acting on the opposite sides of each piston.

A control valve for a variable displacement compressor is known (see e.g. Japanese Unexamined Patent Publication (Kokai) No. 2001-132650 (Paragraph numbers [0043] to [0045], FIG. 4)) which is disposed between a discharge chamber and a crankcase of the compressor, or between the crankcase and a suction chamber of the compressor, for adjusting pressure in the crankcase by changing the flow rate of refrigerant introduced from the discharge chamber into the crankcase, or changing the flow rate of refrigerant delivered from the crankcase to the suction chamber.

The control valve described in Japanese Unexamined Patent Publication (Kokai) No. 2001-132650 is configured such that it has a valve section disposed in a refrigerant passage between the discharge chamber and the crankcase of the compressor when it is mounted in the compressor, and a path is formed along which refrigerant flows from the discharge chamber to the suction chamber of the compressor via an orifice provided between the crankcase and the suction chamber. The control valve has the valve section which comprises a valve element that receives discharge pressure Pd in the valve-opening direction, and a piston rod that is integrally formed with the valve element on a rear side of the valve element and has approximately the same diameter as that of a valve hole, and is configured such that an end face of the piston rod receives suction pressure Ps and the load of a solenoid for setting the discharge capacity of the compressor by an external signal, in the valve-closing direction. Therefore, in this control valve, the discharge pressure Pd and the suction pressure Ps are received by the opposite ends of the valve element and piston rod, both having the same effective pressure-receiving area, and hence the differential pressure (Pd−Ps) between the discharge pressure Pd and the suction pressure Ps causes the valve element to perform an opening/closing operation to thereby control the flow rate of refrigerant flowing from the discharge chamber into the crankcase.

For example, as the rotational speed of the compressor increases with an increase in the rotational speed of the engine to cause an increase in the discharge capacity of the compressor, the discharge pressure Pd increases and the suction pressure Ps decreases to increase the differential pressure (Pd−Ps). This increases the valve lift of the valve section which operates depending on the differential pressure (Pd−Ps), so that the control valve increases the flow rate of refrigerant being introduced into the crankcase to increase pressure Pc in the crankcase, which decreases the discharge capacity of the compressor, thereby decreasing the differential pressure (Pd−Ps). In short, the control valve controls the flow rate of refrigerant being introduced into the crankcase such that the differential pressure (Pd−Ps) between the discharge pressure Pd and the suction pressure Ps is held at a predetermined value. The predetermined value of the differential pressure can be set from outside by a value of electric current supplied to the solenoid.

In the control valve for the variable displacement compressor that operates based on the differential pressure (Pd−Ps) between the discharge pressure Pd and the suction pressure Ps, when the rotational speed of the engine has changed to change the rotational speed of the compressor, causing a change in the discharge capacity of the compressor, the pressure Pc in the crankcase is adjusted after the differential pressure (Pd−Ps) is changed due to the change in the discharge capacity of the compressor. Therefore, when the engine is in a transient period in which the rotational speed of the engine has rapidly changed, the discharge capacity of the compressor can be temporarily largely changed due to low responsiveness of the compressor. This inconvenience can be eliminated by improving the sensitivity of the control valve.

However, the control valve for the variable displacement compressor, which operates based on the differential pressure (Pd−Ps), has a structure in which the load of the solenoid is applied to the piston rod in a manner against the high discharge pressure Pd which the valve element receives, and hence the method of increasing sensitivity by increasing the pressure-receiving area is impractical since the load of the solenoid has to be increased, which makes the solenoid very large in size.

SUMMARY OF THE INVENTION

The present invention has been made in view of the problem, and an object thereof is to provide a control valve for a variable displacement compressor, which is capable of promptly restoring the compressor to a predetermined discharge capacity even when the rotational speed of an engine has rapidly changed.

To solve the above problem, the present invention provides a control valve for a variable displacement compressor, which is configured to sense differential pressure between discharge pressure in a discharge chamber of the compressor and suction pressure in a suction chamber of the compressor, and control a flow rate of refrigerant allowed to flow from the discharge chamber into a crankcase to thereby change a discharge capacity of the refrigerant, comprising a pressure-sensing section that senses a change in pressure caused by a rapid change in a rotational speed of the compressor and accelerates a motion of a valve section in a valve-opening/closing direction performed in response to the change in pressure.

The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to a first embodiment of the present invention.

FIG. 2 is a diagram useful in explaining operation of the control valve, in the case where the rotational speed of the compressor is rapidly increased.

FIG. 3 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to a second embodiment of the present invention.

FIG. 4 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to a third embodiment of the present invention.

FIG. 5 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to a fourth embodiment of the present invention.

FIG. 6 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to a fifth embodiment of the present invention.

FIG. 7 is a central longitudinal cross-sectional view showing a configuration of a control valve for a variable displacement compressor, according to a sixth embodiment of the present invention.

FIG. 8 is an enlarged fragmentary central longitudinal cross-sectional view showing details of essential parts of a control valve for a variable displacement compressor, according to a seventh embodiment of the present invention.

FIG. 9 is an enlarged fragmentary central longitudinal cross-sectional view showing details of essential parts of a control valve for a variable displacement compressor, according to an eighth embodiment of the present invention.

FIG. 10 is an enlarged fragmentary central longitudinal cross-sectional view of the control valve according to the eighth embodiment in an operative state in which the discharge pressure of the compressor has rapidly decreased.

FIG. 11 is an enlarged fragmentary central longitudinal cross-sectional view showing a control valve for a variable displacement compressor, according to a ninth embodiment of the present invention, in states in which the discharge pressure has rapidly increased and in which the discharge pressure has rapidly decreased.

FIG. 12 is an enlarged fragmentary central longitudinal cross-sectional view showing details of essential parts of a control valve for a variable displacement compressor, according to a tenth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to a first embodiment of the present invention.

The control valve 11 comprises a pressure-sensing section 12 that senses a rapid change in discharge pressure Pd, a valve section 13 that senses the differential pressure (Pd−Ps) between the discharge pressure Pd and suction pressure Ps to control the flow rate of refrigerant allowed to flow from a discharge chamber into a crankcase, and a solenoid 14 that is capable of setting a predetermined value to which the differential pressure (Pd−Ps) is to be controlled by the control valve, from outside, these sections being arranged on the same axis.

The pressure-sensing section 12 and the valve section 13 have a first body 15, and a second body 16 into which the first body 15 is press-fitted. The first body 15 has a cylinder 17 that has an open upper end, as viewed in FIG. 1, and the open end defines a high-pressure port 18 communicating with the discharge chamber when the control valve 11 is mounted in the variable displacement compressor. A pressure-sensing piston 19 is disposed within the cylinder 17 in a manner movable axially back and forth, and the pressure-sensing piston 19 is urged downward, as viewed in FIG. 1, by a spring 21 disposed between the pressure-sensing piston 19 and a stopper 20 fixed to an upper end of the first body 15. The cylinder 17 has a hole formed in the center of a bottom thereof, and a hollow cylindrical valve seat-forming member 22 is press-fitted in the hole. The valve seat-forming member 22 has an upper part thereof inserted into a cylinder formed in an center of a lower end the pressure-sensing piston 19, as viewed in FIG. 1, in a recessed manner, thereby defining a pressure-adjusting chamber 23 having an annular space, together with the first body 15 and the pressure-sensing piston 19. The pressure-sensing piston 19 is formed with a through hole which communicates between the cylinder formed in the pressure-sensing piston 19 in a recessed manner and the high-pressure port 18, whereby the high-pressure port 18 communicates with a passage axially extending through the valve seat-forming member 22, i.e. a valve hole, via the through hole of the pressure-sensing piston 19. Further, the pressure-sensing piston 19 has one end of a shaft 24 fixed thereto, the shaft 24 extending through the valve hole defined by the valve seat-forming member 22.

The valve seat-forming member 22 has a lower end, as viewed in FIG. 1, which forms a valve seat, and a valve element 25 is disposed in a manner opposed to the valve seat such that the valve element 25 can open and close the valve hole. The valve element 25 is formed integrally with a piston rod 26, and the piston rod 26 is held by the second body 16 in a manner movable axially back and forth. The piston rod 26 is formed such that it has an outer diameter equal to the inner diameter of the valve hole of the valve seat-forming member 22. The valve element 25 is in abutment with the other end of the shaft 24 which is disposed within the valve hole of the valve seat-forming member 22 and urged downward by the spring 21, as viewed in FIG. 1. Further, the piston rod 26 is urged by a spring 27 in a direction in which the valve element 25 is moved away from the valve seat-forming member 22. It should be noted that a space where the valve element 25 is disposed communicates with a medium-pressure port 28 for supplying pressure Pc to the crankcase of the compressor when the control valve 11 is mounted in the compressor, and a space where the spring 27 is disposed communicates with a low-pressure port 29 for receiving the suction pressure Ps from a suction chamber.

The second body 16 has a hole formed in the center of a lower part thereof, as viewed in FIG. 1. The rim of an opening of a bottomed sleeve 30 is tightly connected to the hole. The bottomed sleeve 30 has a core 31 and a plunger 32 of the solenoid 14 arranged therein. The core 31 is fixed to the hole of the second body 16 and the bottomed sleeve 30 by press-fitting. The plunger 32 is axially slidably disposed in the bottomed sleeve 30, and fixed to one end of a shaft 33 disposed in a manner axially extending through the core 31. Further, the plunger 32 is urged toward the core 31 by a spring 34 such that the other end of the shaft 33 is brought into abutment with a lower end face of the piston rod 26, as viewed in FIG. 1. Disposed around the outer periphery of the bottomed sleeve 30 is a coil 35, and a harness 36 for supplying electric current to the coil 35 is led to the outside of the solenoid 14.

In the control valve 11 constructed as above, the spring 27 urging the piston rod 26 of the valve section 13 toward the solenoid 14 is set to have a larger spring load than that of the spring 34 urging the shaft 33 of the solenoid 14 toward the valve section 13. Therefore, when the solenoid 14 is not energized, the valve element 25 of the valve section 13 is away from the valve seat-forming member 22, and hence the valve section 13 is held in the fully open state. At this time, high-pressure refrigerant at the discharge pressure Pd, which has been introduced from the discharge chamber of the compressor to the high-pressure port 18, passes through the valve section 13 in the fully open state, and flows from the medium-pressure port 28 into the crankcase. This makes the pressure Pc in the crankcase close to the discharge pressure Pd, whereby the compressor is caused to operate with the minimum discharge capacity.

When an automotive air conditioner is started or when the cooling load is maximum, the value of electric current supplied to the solenoid 14 is maximum. At this time, the plunger 32 is attracted with the maximum attractive force by the core 31, so that the piston rod 26 of the valve section 13 is pushed by the shaft 33 fixed to the plunger 32, in the valve-closing direction against the urging force of the spring 27, whereby the valve element 25 is seated on the valve seat-forming member 22 to place the valve section 13 in the fully closed state. At this time, the high-pressure refrigerant at the discharge pressure Pd, introduced into the high-pressure port 18, is blocked by the valve section 13 in the fully closed state, which makes the pressure Pc in the crankcase close to the suction pressure Ps, whereby the compressor is caused to operate with the maximum discharge capacity.

Now, when the value of electric current supplied to the solenoid 14 is set to a predetermined value, the valve element 25 is stopped at a valve lift position where the loads of the springs 21 and 27 urging the valve element 25 in the valve-opening direction, the load of the solenoid 14 urging the valve element 25 in the valve-closing direction, the discharge pressure Pd which the valve element 25 receives in the valve-opening direction, and the suction pressure Ps which the valve element 25 receives in the valve-closing direction are balanced.

In the above balanced state, when the rotational speed of the compressor is increased e.g. by an increase in the rotational speed of the engine, to increase the discharge capacity of the compressor, the discharge pressure Pd increases and the suction pressure Ps decreases so that the differential pressure (Pd−Ps) increases to cause a force in the valve-opening direction to act on the valve element 25 and the piston rod 26, whereby the valve element 25 is lifted, thereby allowing refrigerant to flow from the discharge chamber into the crankcase at an increased flow rate. As a result, the pressure Pc in the crankcase is increased to cause the compressor to operate in a direction in which the discharge capacity thereof is reduced, whereby the differential pressure (Pd−Ps) is controlled to the predetermined value set by the solenoid 14. When the rotational speed of the engine has decreased, the control valve operates oppositely to the above, whereby the compressor is controlled such that the differential pressure (Pd−Ps) becomes equal to the predetermined value set by the solenoid 14.

As described above, when the rotational speed of the compressor is being gently changed as in the case where an automotive vehicle is cruising at an approximately constant speed, the pressure-sensing section 12 is insensitive, and performs the same operation as that of the conventional control valve for a variable displacement compressor. Next, a description will be given of operation of the control valve 11 in the case where the rotational speed of the compressor is rapidly changed by a rapid change in the rotational speed of the engine as in the case where the automotive vehicle has been rapidly accelerated or decelerated.

FIG. 2 is a diagram useful in explaining operation of the control valve for a variable displacement compressor, in the case where the rotational speed of the compressor is rapidly increased.

When the compressor is stably operating e.g. at a rotational speed of 800 rpm, if the rotational speed has been increased up to a rotational speed of 2000 rpm, the valve lift is increased due to a rise in the discharge pressure Pd and a drop in the suction pressure Ps, and as a result, the control valve 11 tends to increase the pressure Pc in the crankcase, as indicated by broken lines in FIG. 2. At this time, the pressure-sensing section 12 receives the discharge pressure Pd, which has rapidly increased, at the pressure-sensing piston 19 having a larger pressure-receiving area than that of the valve element 25. On the other hand, in the pressure-adjusting chamber 23, pressure Pd(av), which is average pressure of the discharge pressure Pd before it has rapidly increased, is maintained, and hence the differential pressure (Pd−Pd(av)) generates a force which acts on the pressure-sensing piston 19 in a direction in which the pressure-sensing piston 19 is moved toward the valve section 13. This force is applied to the valve element 25 via the shaft 24, and hence in addition to the rapidly increased discharge pressure Pd, the differential pressure (Pd−Pd(av)) of the pressure-sensing section 12 is additionally applied to the valve element 25. As a result, as indicated by solid lines in FIG. 2, the valve lift is increased more promptly, so that the control valve 11 causes the pressure Pc in the crankcase to increase more promptly. After that, in the pressure-sensing section 12, the rapidly increased discharge pressure Pd is promptly introduced into the pressure-adjusting chamber 23 via the clearance between the cylinder 17 and the pressure-sensing piston 19 and the clearance between the pressure-sensing piston 19 and the valve seat-forming member 22, whereby the differential pressure (Pd−Pd(av)) becomes equal to zero. At this time, the function of the pressure-sensing section 12 has been lost. This means that the pressure-sensing section 12 has the function of a derivative element for sensing a rapid increase in the discharge pressure Pd, and temporarily accelerating the motion of the valve section 13 in the valve-opening direction. This enables the control valve 11 to promptly restore the compressor to the predetermined discharge capacity.

Although the above description has been given of the operation of the control valve 11 in the case of the rotational speed of the compressor being rapidly increased, the control valve 11 operates similarly when the rotational speed of the compressor is rapidly decreased. More specifically, when the rotational speed of the compressor is rapidly decreased, the differential pressure (Pd(av)−Pd) acting on the pressure-sensing section 12 causes the pressure-sensing piston 19 to move away from the valve section 13, and hence the urging force of the spring 21 urging the valve element 25 in the valve-opening direction via the pressure-sensing piston 19 and the shaft 24 is weakened, which causes the valve element 25 to move in the valve-closing direction. After all, when the rotational speed of the compressor is rapidly decreased as well, the control valve 11 operates in a quite an opposite way compared with the case of the rotational speed of the compressor being rapidly increased.

However, when the rotational speed of the variable displacement compressor is rapidly changed, the shaft 24 sometimes moves away from the valve element 25, depending on the setting of the spring 21. In such a case, the speed of motion of the valve element 25 in the valve-closing direction is made slower, so that the valve-opening characteristic of the control valve becomes an asymmetric one in which the valve opens differently between when the rotational speed of the compressor is rapidly increased and when the same is rapidly decreased. In this case, when the rotational speed of the compressor is rapidly increased as when the automotive vehicle is rapidly accelerated, if the discharge capacity of the compressor is not promptly decreased, the load of the compressor applied to the engine becomes more significant to the engine, whereas in the opposite case, even if the discharge capacity of the compressor is not promptly increased, the load of the compressor applied to the engine only decreases the speed of the automotive vehicle, and hence there is no problem even if the valve opening characteristic is asymmetric.

FIG. 3 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to a second embodiment. In FIG. 3, component elements having functions identical or equivalent to those of the component elements shown in FIG. 1 are designated by identical reference numerals, and detailed description thereof is omitted.

As is distinct from the control valve 11 according to the first embodiment, in the control valve 11 a according to the second embodiment, the shaft 24 of the pressure-sensing section 12, the valve element 25 of the valve section 13, and the piston rod 26 are formed integrally with each other, and the spring 21 urging the pressure-sensing piston 19 toward the valve section 13 is eliminated. That is, in the pressure-sensing section 12 and the valve section 13 of this control valve 11 a, the shaft 24, the valve element 25, and the piston rod 26 are formed integrally with each other, and the shaft 24 is fixed to the pressure-sensing piston 19.

With this arrangement, the control valve 11 a is capable of directly exerting influence of the pressure-sensing section 12 on the valve section 13 in both the cases where the rotational speed of the compressor has rapidly increased and where the same has rapidly decreased. That is, when the rotational speed of the compressor is rapidly increased, the control valve 11 a operates in quite the same way as the control valve 11 according to the first embodiment, but when the rotational speed of the compressor is rapidly decreased, the pressure-sensing piston 19 of the pressure-sensing section 12 is capable of directly actuating the shaft 24, the valve element 25, and the piston rod 26 which are integrally formed with each other, in the direction of closing the valve section 13. Therefore, the control valve 11 a is suitable when the valve-opening characteristic is desired to be made symmetric between when the rotational speed of the compressor is rapidly increased and when the same is rapidly decreased.

FIG. 4 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to a third embodiment of the present invention. In FIG. 4, component elements having functions identical or equivalent to those of the component elements shown in FIG. 1 are designated by identical reference numerals, and detailed description thereof is omitted.

As is distinct from the control valve 11 a according to the second embodiment, in the control valve 11 b according to the third embodiment comprises flow rate-adjusting means for adjusting the amount of leakage of refrigerant flowing into or out of the pressure-adjusting chamber 23, at a location between the cylinder 17 of the pressure-sensing section 12 and the pressure-sensing piston 19 and between the pressure-sensing piston 19 and the valve seat-forming member 22. That is, in the control valve 11 b according to the third embodiment, the pressure-sensing piston 19 and the valve seat-forming member 22 have outer peripheries thereof formed with grooves, respectively, and sealing members 37 and 38, such as piston rings, are disposed in the respective grooves. The sealing members 37 and 38 have the shape of a C-shaped ring which is circumferentially partially cut out, and is made of a material low in sliding resistance, such as polytetrafluoroethylene.

As described above, in the pressure-sensing piston 12, the sealing members 37 and 38 are arranged between the cylinder 17 and the pressure-sensing piston 19 and between the pressure-sensing piston 19 and the valve seat-forming member 22, and the circumferential length of each of cut-off portions of the members 37 and 38 are adjusted, whereby the flow rate of refrigerant flowing from the high-pressure port 18 into the pressure-adjusting chamber 23 or the flow rate of refrigerant flowing out from the pressure-adjusting chamber 23 to the high-pressure port 18 can be adjusted. This makes it possible to adjust the rise and fall characteristics of the valve lift.

FIG. 5 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to a fourth embodiment of the present invention. In FIG. 5, component elements having functions identical or equivalent to those of the component elements shown in FIG. 1 are designated by identical reference numerals, and detailed description thereof is omitted.

As is distinct from the control valves 11, 11 a, and 11 b according to the first to third embodiments which are configured to sense a rapid change in the discharge pressure Pd for control of the valve lift of the valve section 13, the control valve 11 c according to the fourth embodiment is configured to sense a rapid change in pressure Pc supplied to the crankcase for control of the valve lift of the valve section 13.

To this end, in the control valve 11 c according to the fourth embodiment, the pressure-sensing section 12 is disposed between the valve section 13 and the solenoid 14, and the pressure-sensing piston 19 that receives the pressure Pc is fixed to the piston rod 26 integrally formed with the valve element 25. Then, in the pressure-adjusting chamber 23 having an annular shape, which is defined by the first body 15 having the cylinder 17 formed in an end face thereof toward the valve section 13, and the pressure-sensing piston 19, there is disposed a spring 39 for urging the piston rod 26 in the valve-opening direction via the pressure-sensing piston 19 against the discharge pressure Pd.

When the control valve 11 c constructed as above is controlling the compressor to a predetermined valve lift, if the discharge pressure Pd rapidly increases and the suction pressure Ps rapidly decreases, the differential pressure (Pd−Ps) between the opposite ends of the valve element 25 and the piston rod 26 increases, whereby the valve lift is increased. This causes the pressure Pc on the downstream side of the valve section 13 as well to rapidly increase. At this time, since the pressure-sensing piston 19 of the pressure-sensing section 12 has a sufficiently larger pressure-receiving area than that of the valve element 25, a force is generated which causes the pressure-sensing piston 19 to further move in a direction away from the valve section 13, and the force causes the piston rod 26 fixed to the pressure-sensing piston 19 to act in the valve-opening direction. Therefore, the force of the pressure-sensing piston 19 acting in the valve-opening direction is additionally applied to the valve element 25, and thereby causes the valve lift to promptly increase, and hence the discharge pressure Pd and the pressure Pc in the crankcase to sharply increase. In a short time, when the pressure in the pressure-adjusting chamber 23 becomes equal to the pressure Pc in the crankcase, the discharge pressure Pd, the pressure Pc in the crankcase, the suction pressure Ps, and the valve lift promptly returns to their original states. Of course, also when the rotational speed of the compressor is rapidly decreased, the control valve 11 c operates promptly, similarly to the above, to thereby make it possible to promptly restore the compressor to the predetermined discharge capacity.

FIG. 6 is a central longitudinal cross-sectional view schematically showing a control valve for a variable displacement compressor, according to a fifth embodiment of the present invention. In FIG. 6, component elements having functions identical or equivalent to those of the component elements shown in FIG. 1 are designated by identical reference numerals, and detailed description thereof is omitted.

As is distinct from the control valves 11, 11 a, and 11 b according to the first to third embodiments which are configured to sense a rapid change in the discharge pressure Pd for control of the valve lift of the valve section 13, and the control valve 11 c according to the fourth embodiment which is configured to sense a rapid change in pressure Pc supplied to the crankcase for control of the valve lift of the valve section 13, the control valve 11 d according to the fifth embodiment is configured to sense a rapid change in suction pressure Ps for control of the valve lift of the valve section 13.

To this end, in the control valve 11 d, the cylinder 17 is formed in an end face, toward the solenoid 14, of the first body 15 holding the piston rod 26, and in the cylinder 17, there is disposed the pressure-sensing piston 19 which is fixed to the piston rod 26 integrally formed with the valve element 25. Then, in the pressure-adjusting chamber 23 having an annular shape, there is disposed a spring 27 urging the piston rod 26 in the valve-opening direction via the pressure-sensing piston 19.

When the control valve 11 d constructed as above is controlling the compressor to a predetermined valve lift, if the discharge pressure Pd rapidly increases, and the suction pressure Ps rapidly decreases, the differential pressure (Pd−Ps) between the opposite ends of the valve element 25 and the piston rod 26 increases, whereby the valve lift is increased. At this time, since the pressure-sensing piston 19 of the pressure-sensing section 12 has a sufficiently larger pressure-receiving area than that of the valve element 25, a force is generated which causes the pressure-sensing piston 19 to further move in a direction away from the valve section 13, and the force causes the piston rod 26 fixed to the pressure-sensing piston 19 to act in the valve-opening direction. Therefore, the force of the pressure-sensing piston 19 acting in the valve-opening direction is additionally applied to the valve element 25, and thereby causes the valve lift to promptly increase, and hence the pressure Pc in the crankcase to sharply increase, to thereby promptly cause the discharge capacity of the compressor to change in the decreasing direction. In a short time, when the pressure in the pressure-adjusting chamber 23 becomes equal to the suction pressure Ps, the discharge pressure Pd, the pressure Pc in the crankcase, the suction pressure Ps, and the valve lift promptly returns to their original states. Of course, also when the rotational speed of the compressor is rapidly decreased, the control valve 11 c operates promptly, similarly to the above, to thereby make it possible to promptly restore the compressor to the predetermined discharge capacity.

FIG. 7 is a central longitudinal cross-sectional view showing a configuration of a control valve for a variable displacement compressor, according to a sixth embodiment of the present invention. In FIG. 7, component elements having functions identical or equivalent to those of the component elements shown in FIG. 1 are designated by identical reference numerals, and detailed description thereof is omitted.

As is distinct from the control valve 11 according to the first embodiment in which the pressure-sensing section 12 senses rapid changes in the discharge pressure Pd in an increasing direction and a decreasing direction for control of the valve lift of the valve section 13, in the control valve 11 e according to the sixth embodiment, the pressure-sensing section 12 sensitively senses a rapid change in the discharge pressure Pd in the increasing direction but insensitively senses a rapid change in the discharge pressure Pd in the decreasing direction for control of the valve lift of the valve section 13, and a main passage for high-pressure refrigerant does not extend through the pressure-sensing section 12.

More specifically, in the control valve 11 e, the pressure-sensing piston 19 as a component of the pressure-sensing section 12 is provided with a check valve mechanism for switching sensitivity between when a rapid change occurs in the discharge pressure Pd in the increasing direction and when a rapid change occurs in the same in the decreasing direction. The check valve mechanism is formed by forming a passage with a stepped portion in the pressure-sensing piston 19 for communication between the high-pressure port 18 and the pressure-adjusting chamber 23, and disposing a ball-shaped valve element 40 in a large-diameter passage toward the high-pressure port 18. The pressure-sensing piston 19 is urged by a leaf spring 42 engaged with the open end of the cylinder-forming member 41 which is formed integrally with the valve seat-forming member 22 in a manner accommodating the pressure-sensing piston 19, such that the pressure-sensing piston 19 is brought into contact with the shaft 24 that transmits the motion of the pressure-sensing section 12 to the valve element 25 of the valve section 13. The leaf spring 42 also servers to prevent the valve element 40 of the check valve mechanism from being removed from a large-diameter passage in which it is disposed. The shaft 24 is held by the cylinder-forming member 41 with a predetermined clearance therefrom, in a manner movable axially back and forth. Further, the valve hole of the valve seat-forming member 22 directly opens into the high-pressure port 18. Moreover, the first body 15 has a strainer 43 attached thereto such that the strainer 43 covers the high-pressure port 18 including the pressure-sensing section 12.

When the control valve 11 e constructed as above is controlling the compressor at a predetermined valve lift, if the discharge pressure Pd rapidly increases, the check valve mechanism provided in the pressure-sensing piston 19 is closed, so that the pressure-sensing piston 19 having a larger pressure-receiving area than that of the valve element 25 senses a change in the discharge pressure Pd which has rapidly increased, to cause the valve section 13 to rapidly operate in the valve-opening direction, thereby causing the pressure Pc in the crankcase to rise more promptly such that the discharge capacity of the compressor is promptly controlled in the decreasing direction. Inversely, if the discharge pressure Pd has rapidly decreased, the check valve mechanism provided in the pressure-sensing piston 19 is opened by the differential pressure between the rapidly-lowered discharge pressure Pd and pressure in the pressure-adjusting chamber 23, so that the pressure-sensing piston 19 becomes only little sensitive to a change in the rapidly-lowered discharge pressure Pd. This means that the control valve 11 e has asymmetric valve-opening characteristics that it has a high sensitivity to a rapid change in the discharge pressure Pd in the increasing direction, whereas it has a low sensitivity to a rapid change in the discharge pressure Pd in the decreasing direction. Therefore, e.g. even if the compressor performs a transient response to a rapid change in the discharge pressure Pd in the increasing direction to cause the discharge pressure Pd to rapidly change in the decreasing direction, the compressor is prevented from performing a transient response to a rapid change in the discharge pressure Pd in the decreasing direction. This prevents occurrence of a hunting phenomenon.

FIG. 8 is an enlarged fragmentary central longitudinal cross-sectional view showing details of essential parts of a control valve for a variable displacement compressor, according to a seventh embodiment of the present invention. In FIG. 8, component elements identical to those shown in FIG. 7 are designated by identical reference numerals, and detailed description thereof is omitted.

As is distinct from the control valve 11 e according to the sixth embodiment in which the check valve mechanism of the pressure-sensing section 12 is formed using a ball-shaped valve, in the control valve 11 f according to the seventh embodiment, the check valve mechanism of the pressure-sensing section 12 is formed using a poppet valve.

More specifically, in the control valve 11 f, the check valve mechanism provided in the pressure-sensing section 12 is formed by disposing a valve element 40 a in the form of a mushroom in a large-diameter passage toward the high-pressure port 18, which is formed in the pressure-sensing piston 19 such that the passage communicates between the high-pressure port 18 and the pressure-adjusting chamber 23, and urging the valve element 40 a in the valve-closing direction using a spring 44 which is low in load. The operation of the control valve 11 f including the pressure-sensing section 12, constructed as above, is the same as the operation of the control valve 11 e according to the sixth embodiment.

FIG. 9 is an enlarged fragmentary central longitudinal cross-sectional view showing details of essential parts of a control valve for a variable displacement compressor, according to an eighth embodiment of the present invention. FIG. 10 is an enlarged fragmentary central longitudinal cross-sectional view of the control valve according to the eighth embodiment in an operative state in which the discharge pressure of the compressor has rapidly decreased. In FIGS. 9 and 10, component elements identical to those shown in FIG. 8 are designated by identical reference numerals, and detailed description thereof is omitted.

As is distinct from the control valve 11 f according to the seventh embodiment in which the check valve mechanism of the pressure-sensing section 12 is formed using a poppet valve, in the control valve 11 g according to the eighth embodiment, the check valve mechanism is formed using a reed valve.

More specifically, in this control valve 11 g, the check valve mechanism provided in the pressure-sensing section 12 has a through hole formed through the pressure-sensing piston 19 such that the through hole communicates between the high-pressure port 18 and the pressure-adjusting chamber 23, and a valve element 40 b is provided such that the valve element 40 b opens and closes the through hole at an end face of the pressure-sensing piston 19 toward the high-pressure port 18. The valve element 40 b comprises a film-like part which is capable of easily bending in response to the differential pressure between discharge pressure Pd in the high-pressure port 18 and pressure in the pressure-adjusting chamber 23, and a base part fixed to the pressure-sensing piston 19, which are integrally formed of rubber or a flexible resin. The valve element 40 b has the base portion thereof fitted in a fixing through hole formed through the pressure-sensing piston 19, and a portion of the film-like part close to the base part is retained by the leaf spring 42, whereby the valve element 40 b is fixed to the pressure-sensing piston 19.

In the control valve 11 g having the pressure-sensing section 12 constructed as described above, when the rotational speed of the compressor is gently being changed, and when the rotational speed of the compressor is rapidly increased to increase the discharge pressure Pd, the check valve mechanism of the pressure-sensing section 12 is closed as shown in FIG. 9. On the other hand, when the rotational speed of the compressor is rapidly decreased to rapidly decrease the discharge pressure Pd, the check valve mechanism of the pressure-sensing section 12 is opened by the differential pressure between the discharge pressure Pd and the pressure in the pressure-adjusting chamber 23, as shown in FIG. 10.

FIG. 11 is an enlarged fragmentary central longitudinal cross-sectional view showing a control valve for a variable displacement compressor, according to a ninth embodiment of the present invention, in states in which the discharge pressure has rapidly increased and in which the discharge pressure has rapidly decreased. In FIG. 11, component elements identical to those shown in FIGS. 9 and 10 are designated by identical reference numerals, and detailed description thereof is omitted.

The control valve 11 h according to the ninth embodiment is distinguished from the control valve 11 g according to the eighth embodiment, in that the check valve mechanism formed using a reed valve is differently configured.

More specifically, in this control valve 11 h, the check valve mechanism provided in the pressure-sensing section 12 has a valve hole formed by a gap formed around the outer periphery of the pressure-sensing piston 19, and a valve element 40 c disposed such that the valve element 40 c blocks the valve hole from an end toward the high-pressure port 18, with a central portion of the valve element 40 c being held by the leaf spring 42 and the pressure-sensing piston 19 in a sandwiched manner. The valve element 40 c may be formed by a circular film made of rubber or a flexible resin.

When the rotational speed of the compressor is gently being changed, and when the rotational speed of the compressor is rapidly increased to increase the discharge pressure Pd, the valve element 40 c of the check valve mechanism is brought into intimate contact with upper end faces of the pressure-sensing piston 19 and the cylinder in a manner extending over a gap around the outer periphery of the pressure-sensing piston 19 to close the check valve mechanism, as shown in the left half of FIG. 11. On the other hand, when the rotational speed of the compressor is rapidly decreased to rapidly decrease the discharge pressure Pd, the valve element 40 c of the check valve mechanism is bent upward due to the differential pressure between the discharge pressure Pd and the pressure in the pressure-adjusting chamber 23, to open the check valve mechanism, as shown in the right half of FIG. 11.

FIG. 12 is an enlarged fragmentary central longitudinal cross-sectional view showing details of essential parts of a control valve for a variable displacement compressor, according to a tenth embodiment of the present invention. In FIG. 12, component elements identical to those shown in FIG. 11 are designated by identical reference numerals, and detailed description thereof is omitted.

As is distinct from the control valves 11 e to 11 h according to the sixth to ninth embodiments which have the check valve mechanism, the control valve 11 i according to the tenth embodiment includes a sensitivity-switching mechanism which is capable of switching sensitivity between when the discharge pressure Pd rapidly increases and when the same rapidly decreases.

More specifically, in the control valve 11 i, the sensitivity-switching mechanism provided in the pressure-sensing section 12 switches ease of flow of refrigerant flowing into or out of the pressure-adjusting chamber 23, and the outer peripheral shape of the pressure-sensing piston 19 is formed into a tapered shape in which the outer diameter of the pressure-sensing piston 19 progressively decreases from the side toward the high-pressure port 18 to the pressure-adjusting chamber 23. Therefore, a gap between the outer periphery of the pressure-sensing piston 19 and the body 15 provides a narrowest restriction at an upper end of the gap, as viewed in FIG. 12, and is progressively increased in passage cross-sectional area from the restriction to the pressure-adjusting chamber 23. Assuming that the cross-sectional area of the refrigerant passage is suddenly expanded on the high-pressure port 18 side of the restriction, and refrigerant flows from the restriction into the suddenly-expanded portion, a contracted flow is produced there. The pressure-sensing section 12 has a characteristic that insofar as the differential pressure between pressure in the high-pressure port 18 and pressure in the pressure-adjusting chamber 23 is the same, the flow rate of refrigerant is smaller when refrigerant having entered the high-pressure port 18 passes through a restriction after being suddenly restricted in flow than when refrigerant in the pressure-adjusting chamber 23 passes through the restriction after being progressively restricted in flow.

When the rotational speed of the compressor is rapidly increased to thereby rapidly increase the discharge pressure Pd, refrigerant is about to flow from the side toward the high-pressure port 18 into the pressure-adjusting chamber 23 through the gap between the outer periphery of the pressure-sensing piston 19 and the body 15. Inversely, when the rotational speed of the compressor is rapidly decreased to rapidly decrease the discharge pressure Pd, refrigerant is about to flow from the pressure-adjusting chamber 23 toward the high-pressure port 18 through the gap around the outer periphery of the pressure-sensing piston 19. In this regard, there is a difference in the flow rate of refrigerant flowing through the gap between when the discharge pressure Pd has rapidly increased and when the same has rapidly decreased. Therefore, a force which the pressure-sensing piston 19 exerts on the valve element 25 of the valve section 13 in the valve-opening direction when the discharge pressure Pd has rapidly increased can be made larger than a force which the pressure-sensing piston 19 exerts on the valve element 25 of the valve section 13 in the valve-closing direction when the discharge pressure Pd has rapidly decreased.

The control valve for a variable displacement compressor, according to the present invention, is configured such that when the compressor undergoes a rapid change in the rotational speed thereof, the pressure-sensing section senses a change in pressure caused by the rapid change in the rotational speed of the compressor and accelerates the motion of the valve section in the valve-opening/closing direction performed in response to the change in pressure. This is advantageous in that the sensitivity of the control valve can be enhanced only when the compressor undergoes a rapid change in the rotational speed thereof.

The foregoing is considered as illustrative only of the principles of the present invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and applications shown and described, and accordingly, all suitable modifications and equivalents may be regarded as falling within the scope of the invention in the appended claims and their equivalents. 

1. A control valve for a variable displacement compressor, which is configured to sense differential pressure between discharge pressure in a discharge chamber of the compressor and suction pressure in a suction chamber of the compressor, and control a flow rate of refrigerant allowed to flow from the discharge chamber into a crankcase to thereby change a discharge capacity of the refrigerant, comprising: a pressure-sensing section that senses a change in pressure caused by a rapid change in a rotational speed of the compressor and accelerates a motion of a valve section in a valve-opening/closing direction performed in response to the change in pressure.
 2. The control valve according to claim 1, wherein the pressure-sensing section comprises a pressure-sensing piston that is disposed in a high-pressure port through which the discharge pressure is introduced, for receiving the discharge pressure at a pressure-receiving area larger than that of a valve element of the valve section, and a shaft that transmits an axial motion caused by differential pressure between the discharge pressure received by the pressure-sensing piston and pressure in a pressure-adjusting chamber closed by the pressure-sensing piston, through a valve hole to the valve element.
 3. The control valve according to claim 2, wherein the shaft is formed integrally with the valve element that receives the discharge pressure at one end face thereof, and a piston rod that receives the suction pressure at an end face thereof opposite to the one end face.
 4. The control valve according to claim 2, wherein the pressure-sensing piston has flow rate-adjusting means for adjusting an amount of leakage of the refrigerant between the high-pressure port and the pressure-adjusting chamber.
 5. The control valve according to claim 4, wherein the flow rate-adjusting means is a C-shaped ring that is disposed on a sliding surface of the pressure-sensing piston, and has a shape cut out over a circumferential length corresponding to the amount of leakage, the C-shaped ring being made of a material which is low in sliding resistance.
 6. The control valve according to claim 1, wherein the pressure-sensing section has a pressure-sensing piston that is disposed in a medium-pressure port from which control pressure controlled by the valve section is delivered into the crankcase, and receives the control pressure at a pressure-receiving area larger than that of the valve element, and wherein the pressure-sensing piston transmits an axial motion caused by differential pressure between the control pressure received by the pressure-sensing piston and pressure in the pressure-adjusting chamber closed by the pressure-sensing piston, to the valve element.
 7. The control valve according to claim 1, wherein the pressure-sensing section has a pressure-sensing piston that is disposed in a low-pressure port into which the suction pressure is introduced, and receives the suction pressure at a pressure-receiving area larger than that of the valve element, and wherein the pressure-sensing piston transmits an axial motion caused by differential pressure between the suction pressure received by the pressure-sensing piston and pressure in the pressure-adjusting chamber closed by the pressure-sensing piston, to the valve element.
 8. The control valve according to claim 2, wherein the pressure-sensing section has sensitivity-switching means for making a force that the pressure-sensing piston exerts on the valve element larger when the discharge pressure has rapidly increased than when the discharge pressure has rapidly decreased.
 9. The control valve according to claim 8, wherein the sensitivity-switching means is a check valve disposed in a passage formed through the pressure-sensing piston for communication between a side toward the high-pressure port and the pressure-adjusting chamber, for blocking flow of refrigerant from the side toward the high-pressure port to the pressure-adjusting chamber, and allowing flow of the refrigerant from the pressure-adjusting chamber to the side toward the high-pressure port.
 10. The control valve according to claim 8, wherein the sensitivity-switching means is a check valve that has a film-like valve element disposed such that the film-like valve element blocks a gap formed around an outer periphery of the pressure-sensing piston from a side toward the high-pressure port, for blocking flow of the refrigerant from the side toward the high-pressure port to the pressure-adjusting chamber via the gap, and allowing flow of the refrigerant from the pressure-adjusting chamber to the side toward the high-pressure port.
 11. The control valve according to claim 8, wherein the sensitivity-switching means is constructed by forming an outer periphery of the pressure-sensing piston into a tapered shape such that a flow passage cross-sectional area of a gap formed around the outer periphery of the pressure-sensing piston progressively increases from the side toward the high-pressure port to the pressure-adjusting chamber. 